The present invention relates to the detection of electromagnetic radiation in the 80 GHz to 4 THz range. This region of the electromagnetic spectrum has potential for a wide range of medical, pharmaceutical and communications commercial applications as well as being scientifically useful across a wide variety of research fields. Whilst THz systems have been constructed they generally use large and expensive pulsed lasers to generate pulsed THz radiation. While several techniques have been put forward for detecting THz radiation, such as electro-optic sampling, photoconductive sampling and use of bolometers, they are complicated by the need for the pulsed lasers and/or cryogenic cooling.
High speed electroabsorption effects have previously been used to detect THz radiation by W. Sha et al, (Appl. Phys. Lett. 61 (15), 12 Oct. 1992). In Sha et al's scheme the THz radiation was propagated directly onto the multiple quantum well absorber region of the THz detector. In Sha et al's scheme the optical probe signal was a train of 75 fs pulses focussed onto the sample using a lens from a direction perpendicular to the plane of the multiple quantum well absorber region.
In co-pending patent applications GB 0502108.4 and PCT/GB2006/000360, a novel means of extending the operating frequency of optical modulators was outlined and it was stated that such a device could be used to detect radiation in the frequency range 80 GHz to 2 THz. The present invention builds upon this idea by outlining, at least in the preferred embodiments, a promising approach for high sensitivity detection of radiation typically in the frequency range 80 GHz to 2 THz using a high bandwidth optical modulator.